1. Field of the Invention
The invention relates to the field of power electronics. It is based on a converter module and a converter as claimed in the preamble of claims 1 and 10.
2. Discussion of Background
The invention relates to converter modules for high-capacity converters. The converter modules are constructed from a plurality of power semiconductor switches, by means of a busbar system. Such busbar systems have been described, for example, in the article "GTO-Hochleistungsstromrichter fur Triebfahrzeuge mit Drehstromantrieb" GTO high-capacity converters for traction vehicles using three-phase drives!, ABB Technology 4/1995, pages 4-13. Power is supplied to electrically propelled locomotives via a DC intermediate circuit which is coupled on the input side to a DC network or via a mains converter to an AC network and, on the output side, supplies electrical power of variable amplitude and frequency to the three-phase asynchronous traction motors via an in general multiphase drive converter. The busbar system forms the electrical connection between the output of the mains converter--or the overhead wire for a DC network--and the power semiconductor switches or modules of the drive converter. This may be highly complex, may limit the performance of the electrical switching system, and may result in considerable costs.
In the course of development of power semiconductor switches, a change has been made from conventional thyristors or gate turn off thyristors (GTOs) to IGBTs (bipolar transistors with an insulated gate) The IGBTs are in general integrated in a module.
For relatively high currents and ratings, a plurality of modules are connected in parallel. With respect to converter families of various ratings, busbar systems are sought which allow a multiphase converter which can be designed to be modular, can be scaled easily and has low inductance.
It has been proposed in two earlier German Patent Applications (file references 196 00 367.9 and 196 12 839.0), which do not have priority, that this problem be solved by a two-dimensional arrangement of power semiconductor modules over flat DC plates and parallel phase busbars. The flat modules have plug-in contacts extending longitudinally along a narrow, long edge and are pushed into two rows per busbar of lugs, which act as mating connections, parallel to the phase busbars. The closest neighbors are in each case rotated through 180.degree. and are connected to one another in a bridge circuit. They thus form half-bridges or bridge arm pairs, that is to say they make contact with opposite DC plates and feed current half-cycles of opposite polarity into a common phase busbar. The next-but-one neighbors are, in contrast, oriented in the same direction and form parallel-connected modules for power scaling.
This configuration still has disadvantages, such as unsatisfactory symmetry, non-ideal inductance and, in particular, structural complexity. The long, different current paths to and between the modules result in current asymmetries and uneven loads on the modules. The resultant suboptimum utilization increases as the power level or the number of modules per phase increases, which necessitates power derating. Other problems with this arrangement relate to the design aspects. A large number of different parts are required for a type range, and assembly is complex. Compliance with the minimum insulation separations and creepage distances requires particular care since the positive and negative connections are very close to one another and penetrate one another. In addition, tailor-made metal sheet sizes and individually matched components are required for each application and rating level.
According to DE 44 02 425 A1 it is, furthermore, prior art for an invertor arrangement to connect a plurality of bridge arm pairs of semiconductor switching elements in parallel along one phase busbar. The elements in each bridge arm are oriented front to back or facing away from one another or the same, and are made contact with and screwed together via longitudinal profiles. One special feature is that the phase busbar is folded up at the end and is passed back parallel, in order to reduce the inductance.